Modulation



April 14, 1925.

w. A M DONALD MODULATIUN Fild Nov. 12, 1920 Patented Apr 14, 1925.

UNITED STATES WIlILIAM A. MACDONALD, on HTARTSDALE, NEW YORK. MODULATION.

Application filed November 12, 1920. Serial No. 423,536.

To all whom it may concern:

Be it known that I, WILLIAM A. Mac- DGNALD, a citizen of the United States, residing at Hartsdale, in the county of estchester, State of New York, have invented certain new and useful Improvements in Modulation following to be a full, clear, and exact de seription of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

his invention has for its object the provision of an i1 iproved method and apparatus for obtaining unusually effective and ethcient H'lOdlllEltlOIl of the carrier frequency electrical oscillations in a wave signalling system Without producing variations in the frequency of the carrier wave.

The particular advantages gained, as well as the diificulties overcome, by the present invention, will be understood from the following explanation: At the present time,

ree general methods of controlling or modulating high frequency oscillations are in general use, namely, so-called absorption methods,- grid control and plate control.

f the absorption methods the most common are the varying of the amplitude of low power high frequency oscillations or carrier frequency, by a microphone inserted in the output line or radiating circuit, according to whether a so-called wiredwireless system or radio signaling system is employed. For higher powers, the absorption of the unmodulated antenna or output current is generally effected by an appropriate number of vacuum tubes or valves.

Grid modulation has been employed to some extent but with only fair success because of its inherent inelliciency. It is accomplished in the case of telephony, for example, by inserting a microphone and an audio frequency or speech transformer in the grid circuit of a three-element valve. lVhen speech is impressed on the micro phone, the potential of the grid is thrown either positive or negative with respect to its normal potential, thereby varying the load on the late and consequently the output of the tribe.

The circuit arrangement employed with plate control or modulation is generally referred to as the constant current system. In this system one or more tubes are used as and I do hereby declare the.

almost zero, thereby making available for the oscillator twice is varied the voltage when the resistance of. the modulater is infinity and practically nothing when the resistance falls :1 The effectiveness of constant current modulation depends to a presence and character in the circuit, be effected if have ample electron emission ment.

All of the above-mentioned methods of control are limited by the ditliculty of maintaining the carrier frequency constant, since the' modulation in each casewill cause variations of the frequency of the oscillations generated by the oscillator. Moreover, it is a well known fact that in continuous or undamped wave signaling systems Where the signal is received by virtue of of the incoming at1on will not tube does not from the filaand hence in the incoming energy will cause perceptible and objectionable changes in the received note, in many cases a total loss of signal. This, of course, is less pronounced in radio telephony or buzzer-modulated radio telegraphy, butit is a very objectionable feature.

It has heretofore been proposed to use an oscillator Whose output is modulated in accordance with the desired signal or with speech in the case of telephony, plify the resulting modulated oscillations by means of a power amplifier. This arrangement, however, is characterized by troublesome variations in the frequency of the amplified modulated-oscillations produced as a result of the modulation of the oscillator, as explained above.

A solution for the troublesome variations in the carrier frequency produced b modulation lies in the use of a so-callecl master oscillator or frequency-setter, the frequenc of the oscillations which are produced thereby being incapable of variation regardless of its association with suitable modulating means. To this end and inaccord'ance with the present invention, a method and appahnost to zero.

great extent upon the of a suitable choke ClICUlt 2. 3 so as as will be wherein a master oscillator on frequency setter is employed whose frequenc of oscillation is unvaried by the action 0 the modulating means. A convenient manner of obtainin a source of constant frequency controlla 1c high frequency. supply ies in the use of a regenerative vacuum tube oscillator associated in a suitable manner-with the input side of a vacuum tube power amplifier, the oscillations beinggreferably impressed upon the grid or gri s of the vacuum amplifien, A suitable numberof modulating tubes may then be associated with the power amplifier and arranged to modulate its constant frequency output by 0 eratin on the output circuit or plates of t e amp ifying tubes. The modulator in this case cannot vary or change the f quency of the amplified oscillations, and for reasons which can be easily shown by demonstrable. experimental superior ratus is provided facts, modulation of the constant-frequency carrier lVith this arrangement, radio, telephony, practically with eifective and efficient car- a'rticularly in erfect speech 7 modulation of the constant frequency rier wave is readily obtainable.

Circuit arrangements which may be used for the purpose of carrying outthe invention, as well as tages thereof will be understod from the accompanying draw1ngs and the following detail description.

I these drawings: ..Fig. 1 illustrates a diagrammatic circuit arran ement embodying the invention an capable of being operated in accordance withmyimproved method of control; and

- Fig. 2 illustrates a vaccum tube system which operates in accordance with the invention.

Referring now to Fig. 1, a master oscillator or frequency-setter 1 is arranged in the to impress oscillations of the desired frequenc upon the power amplifier 4:. In this way t ie oscillations generate by the, master oscillator may be amplified to any desiredvalue or amplitu e. The resulting amplified oscillations in the output circult 5, (inlay then be controlled or modulated-by the vacuum tube moduator 7, for example, in accordance with speech im pressed on the microphone 8. Other forms of audio frequency modulation may be used understood, for example, the use well known.

of the buzzer is The frequency of carrier wave having been set by the master oscillator l, the modulated signaling energy will be radiated at a constant frequency from the antenna 9 even if variations occur in the electrical constants of the antenna circuit 9, 10. Variations of the electrical constants of the antenna circuit will, however, afiect the value of the antenna current,

oscillator further features and advan ing upon the the oscillations of the eliicient operation of the system. In any event. this choke should present a high impedance with relation to the impedance of the tube or tubes for voice frequencies.

In Fig. 2 a vacuum tube regenerative oscillator ll is provided as a convenient controllable source of high frequency oscillations. The output circuit iii-14 of the master oscillator or frequency-setter 12 is associated with the input or grid circuit 15-46 of the vacuum The tube 18 modulates amplifier by variably diverting the current supply of its plate circuit, 19-20,- in accordance with the known method of constant current modulation. hloreover, because of the fact that the constants of the master are not affected by variations in the amplifier circuit or antenna, carrier oscillations of continuous frequency may be generated and the frequency maintained constant throughout the entire radiating or other transmission portion of the system.

With this system and in accordance with the present invention, the carrier wave may be modulated in accordance with any source of audio frequency oscillations by impress grid circuit 21 22 audio frequency oscillations in accordance with the desired signal, for example, in accordance with speech by means of the microphone 23. It is to he understood, however, that other known audiofrequency devices may be substituted for the microphone. In any case, the transmitted signal energy will be radiated by the antenna system flak-25 and any variations in the electrical constants of this system, will affect only the amplitude of the carrier wave but not its frequency.

As in the case of Fig. 1, a suitable choke coil 26, or bandfilter is located in the posis tive lead of the high voltage input'to the amplifier or modulator tube or tubes.

It is to be understood that while certain embodiments of the invention havebeen i1 lustrated and described herein, ous arrangements of circuits an com nent parts thereof may be varied without epa-rting from the spirit and scope of this invention.

1. In a wave signaling s generating continuous big ricr oscillations, and amp ifier for am lifying said carrier oscillations, a sourceo unidirectional voltage for said amplifier, a variable impedance in series in a direct current circuit with said source of voltage, means for keeping 'the current from said source the output of the the amplitude of the carrier that the variput circuit, a vacuumftuibeamgilififli for a m piifying said fiequeney oscillations, said amplifier having- "an input. circuit? and "an ,output ifcuit, said;input circuit-W ll"? ancewithsignals to be transmitted, iI e-arassociated withrthe said'ontppt circuit ofs' ai generator; iarsour'ce of current the piztp'ut circuit Of SaidamPIifier, aivarifahle-flres s'tance in shunt to'said source ofcurrent; and means' of continuous high constant amplitude; an output circuitfor,

. for Varying said "resistance in accordance- Withsiignalsf 3; In. ww'zives gnaiil igsistem,"a' enerabor said generator aiiacuum-tube amplifier having input electrodes and output electrodes, an input circuit-2 for said "am lifier, said input circuit being associated with the output circuit of. said. genemtor, an' output circuit for saidampiifier including said output electrodes, "a load circuit assoc ated with said output circuit, a source of uni-directiona1 current included in the output circuit of said axnglifier, an inductance coil in series with $8.1 .source of current and included in said output circuit said coil-being operable to maintain the flow of current from said scurce substantially constant,' a second vacuuin tube comprising a plate, a grid and firequency osc' ations of a filament, said plate and filament being connected in series with said source of current and said inductancecoil and in. shunt to the-butput electrodes of amplifier,- "aifiiiput 'circuit foii'said second vacuum tube and a;1n'icrophone :-ass0ciated ivith said last -z nentionedinpiit*circuit andoperableto very late and filap d ce betwe n my aid secondvacuuiii' be'in accordmanta rangement barn? such that continuous high .frequency oscil ati'ons from said generator arejan lified b said a nplifieir'and simultaneous incd atedgbj diversion of current 'froni' sardam lijierinaccordance with signals impresse on said microphone and furtilelfinfll'ethat the frequene of-said oscillas. this issubstantially una ected by varia, tibns'finthe constants of said'load circuit.

41 Themethod of producing signal modulatecl high frequ'encycartier current of sub; stantially uniform frequency which consistsin generating unmodulated'high frequency carrier current of substantially constant fre quency, impressing said unmodula-ted carrier current u on the input circuit of an ampli- 'fier, supp ying current of substantially con-, stant value to the output-circuit of said am-- plifier and variably diverting said cur-rent awayfrom said amplifier in accordance with signals to betransmitted.

In testimony whereof I an my signature.

WILLIAMA. MACDONALD.

Locusts put circuit, a vacuum tube amplifier for 'agnp yi g. said h gh" fi qu y ei st o said amplifier having "an input circuit-inn an .output urcaiasminpat circuit associa generator, a'rsour'ce of current the output circuit of saidamplifier, ayariableflresistance' inshunt tos'a'idsource of-current; and-means of continuous big for varyin'gf sa'id resistance in accordance output circuit of. said. generator, an "-output circuit'for said'almplifier including said output electrodes, a load circuit assoc ated with said output circuit, a source of uni-directiona1 current included in the output circuit of said amfilifier, an nductance coil in series wlth'sai to maintain the flow of current from said 'ran'gement beinF frequency" oscil a 4 f irquency cscillationsof constant amplitude, an output circuit for, said g'eneratoga yacuumtube amplifier havsource of current and included in said output circuit said coil-being operable vsignals to be transmitted. source substantially constant, a'second vacuum tube comprising a plate, a grid and a --filament,'said plate and filament being connected in series with said source of current and said -1nductance.co1l and m shunt to the- "output velectrodes of said. amplifier,

an'iiiput' circuitfor'said second vacuum tube anda m'icrophone (associated; v vith said last mentioned inputfcircuit and operable to vary "the edancc betwcen thefplate and fila- 7 benig f-n ento -said second v cuum" ed withfthe said output circuit ofjsai' l ub' in accord ancewith signals to be transmitted, theatsuch that cont-inuoushigh ti'ons frorn *said generator arejalm ified M tane'ou y mod byydivers'ion of current froni'saidam lijieri-niccordance .with signals impresse "on said microphone and fur: thermore that the frequenc ofsaid oscilla li tionsi's substantially una ected' by" varies tionstfinthe constants of said'load circuit.

, 41 Th'e method of producing sigualmodw 'lated high fre u'encycarrie-r current of sub-u stantially uniorm frega'uency which consists in generating unmodu' 7 carrier currentof substantially constant frequency, impressing said unmodulated carrier at J "66 ated' high frequency current u on the input circuit of an amplifier, supp ying current of substantially con-y stunt value to the out ut-circuit of said tun-- plifier and variably ivert'ing said current awayfrom said amplifier in accordance with V i In testimony whereof I 2am my signature.

WILLIAMA; MACDONALD.

DISCLAIMER.

1,533,'653.--l-Vill1'am Air/lemma,- I-Iartsdale, N. Y.

MpnULA'rIoN. Patent dated April 14,, 1925. Discla mer filed May 28, 1926,.by the 'patentee. Hereby enters this disclaimer to claims 2, 3, and 4 of said Letters Patent, viz..: He disclaims from claims 1, 2; and 3 any generator or means for generating coutinuous high-frequency carrier-oscillations except a vacuum tube system generator producing continuous high frequency oscillations of substantially constant amphtude and frequency, "whereby such oscillations are supplied unmodulatecl to the modulatin amplifier and He disc aims from claim 4 any method of producing signal-modulated highfrequency carrier-current of substantially uniform frequency excepting where the results obtained are the results obtained by the use of a vacuum tube system gem erator producing continuous high frequency flmfllludfi and frequency.

oscillations of substantially constant DISCLAIMER- 1,533,653.-W1'Iliam A. Mun-Donald, l'lurisiluh', Y. Mnoumnux. lnlvut (lulml April 14, 1925. Discla mer filed May 29. 1926, by the patentee.

Hereby enters this disclaimer tn claims I. 2, l, and 4 of Suit] Letters Patent, viz.

He disclaims from claims 1, 2, and 3 any gzvm-rntnr or means for generating mntinuous high-frequency carrier oscillations except a vummm llllnsystem 1 murmur producing continuous high frequency nsrillations of substantially constant amplitude and frequency, whereby such osrillations are supplied uulnodulated to the znodulati amplifierg and He di aim from claim 4 any method of producing signal-modulated highfrequen comer current of substantially uniform fre uency excepting where the med are the results obtained by the use 0 a vacuum tube system gente lts o erator producing continuous high frequency oscillations of substantially ('(lllStflIllZ am litude and frequency.

Oficial Gazette June 15, 19:36.] 

